Radiation transducers are frequently used to provide a communications link between two or more devices in conditions where the devices are required to be electrically isolated or where a standard electrical connection would be unsuitable.
Radiation transducers can function as a communications link between two devices in the following ways: unidirectionally, also known as simplex communication; and bidirectionally in both directions, known as duplex communication.
An example of an application of radiation transducers in a simplex communication system for providing temporary communication between enclosed electronic equipment and a separable control unit is disclosed in U.S. Pat. No. 4,821,215, S. J. Woodward, issued on Apr. 11, 1989 and assigned to the assignee of the present application. The specification of the Woodward patent is incorporated herein by reference. The Woodward patent relates to monitoring equipment for use in adverse or hazardous environments. The Woodward patent discloses a portable dumb keypad equipped with an infrared transmitter for use in communicating with monitoring equipment equipped with an infrared receiver and a display.
In the Woodward patent, simplex communication takes place between the dumb keypad and the process control equipment when the keypad is docked in a recess in the case of the process control equipment. The dumb keypad allows the operator to control and change various parameters of the monitoring device. The monitoring device, on the other hand, is incapable of communicating with the keypad. The keypad is used to retrieve data from the memory of the monitoring unit by means of the display. This technique of retrieving data may be impractical in certain circumstances, particularly when a significant amount of data has been stored by the unit over an extended period of time. Furthermore, it may be impractical, except in the simplest of cases, to use the dumb keypad to program or reprogram the monitoring unit, especially when a plurality of monitoring units must be identically programmed or reprogrammed.
Systems in which bidirectional communication is used between two electrooptically linked devices, each equipped with a transceiver, are disclosed in U.S. Pat. No. 3,503,061, T. E. Bray et al., issued on Mar. 24, 1970 and U.S. Pat. No. 4,119,948, E. M. Ward et al., issued on Oct. 10, 1978.
Communications links, such as electromagnetic, ultrasonic and infrared links, are increasingly being used in a number of applications for monitoring and reprogramming electronically controlled equipment in sealed or tamperproof enclosures. The physical structure of the actual radiation link may take many forms, but in general each type of equipment, or even the same type of equipment from different manufactures, forming one end of such a link requires a customized monitoring and/or programming unit providing the other portion of the link. Such specialized units are expensive, and may not provide for functions such as diagnosis and repair of malfunctioning units, or field testing of units under development. Depending on the application, it may also be necessary to protect the unit against adverse environments, and to ensure that it is intrinsically safe for use in hazardous environments. Such a unit is the Series 847 Portable ENRAF Terminal (PET) available from Enraf-Nonius and adapted to interface through an optical fibre link with gauges manufactured by that company. Such a weatherproof and intrinsically safe product is necessarily expensive to produce, yet is useful only for its own limited purposes. A field engineer on the other hand may need to deal with many types of equipment, and may need facilities beyond those provided by a specialized terminal of this nature.
To enable personal and other computers and controllers having general purpose serial communications ports to communicate with other devices over various types of data links, they are normally used with modems, which convert the serial data to and from a form suitable for communication over the type of data link to be utilized, and provide an interface to and from that data link.